Heat-generating mixture and device and method for heat generation

ABSTRACT

A heat-generating mixture includes 40 to 55 wt % of metal silicide, 40 to 60 wt. % of iron (III) oxide, and 0 to 10 wt. % of silicon. On burning, the heat-generating mixture forms a non-melting, porous slag. In a method of heat generation, to generate heat, an igniter capable of being actuated mechanically or electrically, ignites a booster charge, which in turn ignites the heat-generating mixture. A device for heat generation incudes an igniter capable of being actuated mechanically or electrically, a booster charge and the heat-generating mixture fixed and/or contained in and/or on a casing.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application of U.S. application Ser.No. 10/548,601, filed Sep. 13, 2005, the contents of which areincorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates to a heat-generating mixture and to a method and adevice for heat generation, especially for heating foodstuffs such aswater, coffee, instant meals, etc.

Heat generation by the thermite process is known per se in traditionalwelding technology. However, thermite cannot be used in heat generationfor foodstuffs because it forms a molten ball that can lead tomechanical instability to the point of melting through the casing of thedevice for heat generation.

U.S. Pat. No. 6,267,110 B1 discloses a disposable heating unit for afood container. As the heat-generating mixture, the device disclosed inthis document also contains components that react together spontaneouslyat room temperature when they are brought into contact with one another,at least one of these components being in liquid form.

DETAILED DESCRIPTION OF THE INVENTION

The object of the present invention was therefore to provideheat-generating mixtures that overcome the disadvantages of the state ofthe art.

The solution according to the invention provides a heat-generatingmixture containing one or more of the constituents metal silicide, ironoxide and silicon, optionally together with additives and processingaids such as silicon dioxide or water glass. The heat-generating mixtureaccording to the invention is accommodated in a device which contains,in and/or on a casing, inter alia in addition to the substance to beheated, a booster charge and an igniter capable of being actuatedmechanically or electrically, preferably piezoelectrically. The casingcan be made of metal and/or plastic. If necessary, in the heatgeneration according to the invention, the booster charge is ignited bythe igniter and in turn reliably and uniformly ignites theheat-generating mixture according to the invention. In a suitablemechanical casing, the slow and smoke-free combustion of theheat-generating mixture heats e.g. water. The thermomechanical stresseson the casing are markedly reduced because, on burning, a desirablenon-melting, porous slag is formed in which the beads of iron cannotcombine to form a molten ball. The temperature and the time taken toreach the maximum temperature can be controlled by way of theformulation, the amount of mixture used, the amount of water and/or thetype of mechanical casing. Thus, for example, 25 g of the mixtureaccording to the invention heat 125 ml of water from 20° C. to 98° C.within 60 seconds in a suitable apparatus.

Only solids that do not react with one another at room temperature areused in the heat-generating mixture according to the invention, in theassociated booster charge and in the igniting mixture. Theheat-generating mixture used according to the invention is e.g. amixture containing 40 to 55 wt. % of metal silicide, preferably calciumsilicide and/or iron silicide, 40 to 60 wt. % of iron(III) oxide, 0 to10 wt. % of silicon, and additives and processing aids such as silicondioxide or water glass. The booster charge for the heat-generatingmixture can consist e.g. of mixtures containing light metals such astitanium, magnesium and/or aluminium, and metal silicides such ascalcium silicide and/or iron silicide, iron oxide, silicon andadditives, or other mixtures known from the state of the art. Theigniters used for the booster charge are preferably anvil-shaped ignitercaps that are capable of being actuated mechanically and are based onigniting mixtures free of lead and heavy metals. These are known fromthe state of the art and contain e.g. potassium dinitrobenzo-furoxanateor diazodinitrophenol, tetrazene, zinc peroxide, nitrocellulose, andadditives such as powdered glass and titanium. The heat-generatingmixtures according to the invention are prepared by methods known perse: the components are mixed in the indicated amounts and optionallycompressed. The same applies to the igniting mixture and the boostercharge.

The batch formulations are illustrated by the Examples below withoutthereby limiting the invention:

TABLE 1 Heat-generating mixture: Example 1.1 Example 1.2 Content [wt. %]Calcium silicide Iron silicide 40-55 Iron(III) oxide Iron(III) oxide40-60 Silicon Silicon  0-10 Silicon dioxide Silicon dioxide 0-5 Waterglass Water glass  0-20

TABLE 2 Booster charge: Example 2.1 Example 2.2 Content [wt. %]Magnesium Titanium 10-30  Calcium silicide Calcium silicide 25-35 Silicon Silicon 0-10 Iron(III) oxide Iron(III) oxide 40-55  Additives:Additives: Binder Binder 0-10 Silicon dioxide Silicon dioxide 0-10Graphite Graphite 0-10 Boron nitride Boron nitride 0-10

TABLE 3 Igniting mixture: Example 3.1 Example 3.2 Content [wt. %]Potassium dinitro- Diazodinitrophenol 20-40  benzofuroxanate Zincperoxide Zinc peroxide 20-40  Tetrazene Tetrazene 0-10 Titanium Titanium0-20 Nitrocellulose Nitrocellulose 0-40 Powdered glass Powdered glass0-20

The following compositions may be mentioned as preferred embodimentswithout thereby excluding other possible formulations:

Heat-generating mixture: iron silicide: 48 wt. % iron(III) oxide: 50 wt.% silicon:  2 wt. % Booster charge: magnesium: 20 wt. % calciumsilicide: 30 wt. % silicon:  3 wt. % iron(III) oxide: 47 wt. % Ignitingmixture: potassium dinitro- 30 wt. % benzofuroxanate: zinc peroxide: 25wt. % tetrazene:  5 wt. % titanium:  5 wt. % nitrocellulose: 35 wt. %

The heat-generating mixture according to the invention can be used e.g.to prepare for consumption foodstuffs such as water, coffee, instantmeals, etc., in a suitable device.

1. Heat-generating mixture, comprising 40 to 55 wt % of metal silicide,40 to 60 wt. % of iron (III) oxide, and 0 to 10 wt. % of silicon,characterized in that it, on burning, it forms a non-melting, porousslag.
 2. Heat-generating mixture according to claim 1, characterized inthat, on burning, it does not form a molten ball.
 3. Method of heatgeneration, characterized in that, to generate heat, an igniter capableof being actuated mechanically or electrically, ignites a boostercharge, which in turn ignites a heat-generating mixture according toclaim
 1. 4. Method of heat generation according to claim 3,characterized in that the igniter is actuated mechanically.
 5. Devicefor heat generation, characterized in that an igniter capable of beingactuated mechanically or electrically,a booster charge andheat-generating mixture according to claim 1 are fixed and/or containedin and/or on a casing.
 6. Device for heat generation according to claim5, characterized in that the igniter is an anvil-shaped ignition capcapable of being actuated mechanically.
 7. A method for heatingfoodstuffs comprising actuating the device according to claim 5, andheating foodstuff with the actuated device.
 8. A method for heatingfoodstuffs comprising igniting the heat-generating mixture according toclaim 1, and heating foodstuff with the ignited heat-generating mixture.9. Heat-generating mixture according to claim 1, further comprisingsilicon dioxide and/or water glass.
 10. Heat-generating mixtureaccording to claim 1, characterized in that it contains 45-50 wt. % ofmetal silicide, 45-55 wt. % of iron (III) oxide, and 0 to 5 wt. % ofsilicon.
 11. Method of heat generation according to claim 3,characterized in that the ignition is capable of being actuatedpiezolectrically.
 12. Device for heating generation according to claim5, characterized in that the ignition is capable of being actuatedpiezolectrically.
 13. Heat-generating mixture according to claim 9,characterized in that silicon dioxide is contained in an amount up 5 wt.%.
 14. Heat-generating mixture according to claim 13, characterized inthat water glass is contained in an amount of up to 20 wt. %. 15.Heat-generating mixture according to claim 9, characterized in thatwater glass is contained in an amount of up to 20 wt. %. 16.Heat-generating mixture according to claim 1, characterized in that themetal silicide is calcium silicide and/or iron silicide. 17.Heat-generating mixture according to claim 1, characterized in that themetal silicide is calcium silicide.
 18. Heat-generating mixture,comprising 40 to 55 wt % of iron silicide, 40 to 60 wt. % of iron (III)oxide, and 0 to 10 wt. % of silicon.